Drag Vacuum Pump

ABSTRACT

A friction vacuum pump ( 10 ) comprises a housing ( 12 ) defining a vaneless pump stator ( 30 ), a rotor drive and a rotor support which rotatably supports a pump rotor ( 16 ) provided with a vane ( 18 ). The housing ( 12 ) surrounds the overall axial length of the pump rotor ( 16 ), the rotor drive and the rotor support. Prior art housings are of multipart configuration and thus comprise seals between the housing portions. The seals are difficult to coat and may be or become locations where leaks occur. In contrast, the housing ( 12 ) is of one-piece configuration such that, in any case, the region of the housing ( 12 ) which is in contact with the vacuum gas is free of seals.

BACKGROUND

The invention relates to a friction vacuum pump comprising a housinghaving a vaneless pump stator, a rotor drive and a rotor support.

The housing of such friction vacuum pumps, for example turbomolecularpumps or Holweck pumps, surrounds the overall axial length of the pumprotor, the rotor drive and the rotor support. From US 2005/220607 ascrew pump is known whose housing essentially comprises three axiallyadjacent portions which are joined together, for example screwedtogether, to form a housing. The three housing portions are a statorhousing portion, an outlet housing portion which supports a cartridgecomprising the motor and/or the support, and a bearing housing portion.Between two adjacent housing portions respective seals are arranged forensuring the required tightness, which seals may be difficult to coat orimpossible to coat at all with a corrosion-inhibiting coating material,for example. Even the greatest care taken during the assembly workcannot completely prevent leaks from occurring in the sealing region.Further, the temperature behavior of the overall housing isinhomogeneous due to the multipart configuration of the housing.

From U.S. Pat. No. 6,514,035 a screw pump is known whose housing iscomposed of two portions, wherein the discharge-side housing portion isintegrally formed with a bearing and motor housing. The two-partconfiguration of the housing leads to the aforementioned drawbacks.

It is an object of the invention to improve the physical properties of afriction vacuum pump.

SUMMARY

In the friction vacuum pump according to the invention, the housing isconfigured in one piece over its overall axial length such that theone-piece housing surrounds the overall axial length of the pump rotor,the rotor drive and the rotor support. The one-piece configuration ofthe housing ensures a homogeneous temperature behavior of the housing.Since no seals are provided, tightness of the housing can be ensuredeven over a long term. It is not necessary that the housing itself iscomposed of a plurality of parts, such that no assembly work andresultant sources of defects occur. Since no seals are provided in thehousing region, the housing inside can be easily and continuouslycoated. The friction vacuum pump housing comprises only an end-sidecover, for example, which has no load-bearing function and does thus notrequire any particular precision during assembly work.

The one-piece configuration of the housing improves numerous physicalproperties of the friction vacuum pump, in particular the temperaturebehavior, the tightness and the quality of coating of the housinginside.

According to a preferred aspect, the rotor support and the rotor driveare arranged in a cartridge supported by the housing and surrounded overits overall axial length by the housing. As used herein, the termcartridge refers to a device designed as a cartridge housing which is ofpot-shaped or completely closed configuration and in which a shaft ofthe rotor support is rotatably supported, said shaft being adapted to bedriven by a rotor drive disposed in the cartridge. The support and thedrive are arranged in a completely preassembled condition in the closedor nearly closed cartridge. When assembling the friction vacuum pump,first the shaft extending from the cartridge can be connected with thepump rotor, and this structure can then be inserted into the housing,wherein the cartridge is mounted in the housing interior. In thismanner, the friction vacuum pump can be easily and reliably assembled.The one-piece configuration of the friction vacuum pump housing and theprovision of a single drive and support cartridge result in a modulardesign of the friction vacuum pump. Both features together facilitatethe assembly and disassembly work, which, in turn, improves the assemblyaccuracy, reduces the assembly expenditure, and facilitates andaccelerates the maintenance and repair work.

Preferably, the cartridge comprises a pot-shaped housing which isintegrally formed with the friction vacuum pump. When the rotor supportand the rotor drive are inserted in the pot-shaped housing, the potopening is closed by a cartridge cover. The one-piece configuration offriction vacuum pump housing and pot-shaped cartridge housingfacilitates the assembly work, reduces leaks, and in particular ensuresa more precise positioning of the cartridge and/or the rotor drive andthe rotor support.

According to a preferred aspect, at least 50% of the axial length of thecartridge is surrounded by the pump rotor, i.e. at least half the axiallength of the cartridge axially extends into the pot-shaped pump rotor.In this manner, a friction vacuum pump configuration which is compactwith regard to the overall axial length is realized.

According to a preferred aspect, a portion of the cartridge housing isdefined by the friction vacuum pump housing. The cartridge housingcomprises two sections, i.e. one arranged on the rotor side as seen fromthe mounting location of the cartridge at the housing, and one arrangedremote from the rotor. The cartridge section arranged remote from therotor may be defined by the friction vacuum-pump housing, i.e. thepot-shaped cartridge housing does not comprise a cartridge cover but isterminated by the friction vacuum pump housing. Thus, the total numberof components is reduced.

According to a preferred aspect, the housing comprises a circularshoulder at its inside, against which the cartridge preferably bears onthe suction side and to which the cartridge is fastened. The cartridge,together with the rotor, is inserted into the housing preferably fromthe suction side. The cartridge is placed upon the circular shoulder andfastened by suitable fastening means, for example threaded screws,preferably from the discharge side of the shoulder. The circularshoulder is easy to produce and allows the cartridge to be fastened in agastight manner to the housing.

Preferably, the pump rotor is a Holweck pump rotor. The surface in theradial plane between a housing-side stator wall and a rotor-side hub maydecrease towards the discharge side.

Thus the inlet cross-section of the friction vacuum pump is relativelylarge, which results in a relatively large gas throughput.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described in greater detailwith reference to the drawing.

The FIGURE shows a longitudinal section of the friction vacuum pumpaccording to the invention.

DETAILED DESCRIPTION

The FIGURE shows a friction vacuum pump 10 which is a screw pump, alsoreferred to as a Holweck pump. The friction vacuum pump 10 essentiallycomprises a housing 12 which narrows in a funnel-like manner towards thesuction side, a cartridge 14 arranged and fastened in the housing 12,said cartridge 14 including a rotor support not shown and a rotor drivenot shown, and a pump rotor 16 comprising a plurality of helicallyarranged vanes 18.

The housing 12 is of one-piece configuration and surrounds the overallaxial length of the pump rotor 16 and the cartridge 14 including therotor drive and the rotor support. The discharge-side end of the housing12 is closed by a front-side housing cover 20.

In the housing 14 a circular shoulder 22 is provided at the innercircumference, on which circular shoulder 22 a corresponding circularshoulder 24 of the cartridge 14 is supported in a gastight manner. Theshoulders 22,24 of the housing 12 and the cartridge 14 are screwedtogether.

A rotor shaft 26 extends from the suction side of the cartridge, saidshaft 26 supporting the rotor 16. The rotor 16 is connected with therotor shaft by screwing, for example.

The rotor hub 28 of the rotor 16 tapers towards the suction side. Theinside of the housing 12 forms a stator wall 30 which expands towardsthe suction side. Due to the expansion of the inner diameter of thestator wall and the reduction of the outer diameter of the rotor hub 28towards the suction side, the surface in the radial plane between thestator wall 30 and the rotor hub 28 increases towards the suction sideand decreases towards the discharge side.

The housing 12 comprises a gas inlet 32 at its suction-side axial end. Athe discharge side of the pump rotor 16 a radial gas outlet 34 isprovided.

Due to its one-piece configuration the housing 12, in the portion whereit encloses the vacuum, does not comprise any seal towards an adjacenthousing portion. Thereby, in particular in that region of the housing 12which is exposed to the vacuum, a homogeneous temperature behavior isachieved. Coatings of the stator wall 30 are free from discontinuities.Since no seal is provided between two housing portions, no leaks canoccur.

The invention has been described with reference to the preferredembodiments. Modifications and alterations may occur to others uponreading and understanding the preceding detailed description. It isintended that the invention be constructed as including all suchmodifications and alterations insofar as they come within the scope ofthe appended claims or the equivalents thereof.

1. A friction vacuum pump comprising: a housing forming a vaneless pump stator, and a rotor drive and a rotor support which supports a pump rotor comprising a vane, wherein said housing surrounds the overall axial length of the pump rotor, the rotor drive and the rotor support, and the housing is of one-piece configuration.
 2. The friction vacuum pump according to claim 1, characterized in that wherein the rotor support and the rotor drive are arranged in a cartridge which is supported by the housing and surrounded over its overall axial length by said housing.
 3. The friction vacuum pump according to claim 2, wherein the cartridge comprises a pot-shaped housing which is integrally formed with the friction vacuum pump housing.
 4. The friction vacuum pump according to claim 2, wherein at least 50% of the axial length of the cartridge is surrounded by the pump rotor.
 5. The friction vacuum pump according to claim 2, wherein a portion of the cartridge housing is defined by the friction vacuum pump housing.
 6. The friction vacuum pump according to claim 2, wherein the housing comprises a circular shoulder to which the cartridge is fastened.
 7. The friction vacuum pump according to claim 1, wherein the pump rotor is a screw pump rotor.
 8. The friction vacuum pump according to claim 1, the wherein a surface in a radial plane between a pump stator and a hub of the pump rotor decreases towards a discharge side.
 9. A friction vacuum pump comprising: a funnel-shaped housing which tapers from an inlet end towards a discharge end, the housing being an integral one-piece construction; the one-piece housing including an integrally formed shoulder adjacent the discharge end, the shoulder being in a plane transverse to a central axis of the one-piece housing; a cartridge which houses a rotor drive and a rotor support, the cartridge being supported on the integral shoulder and extending along the central axis of the one-piece housing; a rotor having at least one vane, the rotor being supported on the rotor support and received within the housing.
 10. A method of assembling the friction vacuum pump of claim 9 comprising: inserting the cartridge into the integral, one-piece housing from the inlet end; attaching the cartridge to the flange; attaching the rotor to the rotor support. 